1. Field of the Invention
The present invention relates to a noncontact ultrasonic flaw detecting method and an apparatus therefor, and particularly to a noncontact ultrasonic flaw detecting method utilizing ultrasonic waves generated in materials, wherein the materials to be inspected, such as steel members are irradiated with a laser beam or the like to detect flaws therein and to an apparatus therefor.
2. Description of the Prior Art
A conventional noncontact ultrasonic flaw detecting method comprises steps of instantaneously irradiating a material such as steel member to be inspected with a laser beam, generating ultrasonic waves in the material to be inspected, and generating thermal impact in the irradiated portion of the material (U.S. Pat. No. 4,137,778).
According to the above-mentioned noncontact ultrasonic flaw detecting method wherein the material to be inspected is simply irradiated with a laser beam, the accuracy for detecting a flaw is low since ultrasonic waves are not focused in the material being inspected and the propagation direction is not controlled.
With the contact-type ultrasonic flaw detecting method wherein an ultrasonic probe is pressed on the surface of the material to detect a flaw, an angled ultrasonic wave beam or a focused ultrasonic wave beam is generated in the material to be inspected, in order to detect flaw therein.
However, when the material to be inspected is heated at high temperatures, the ultrasonic probe may be damaged by the heat. Since water, glycerin, oil or the like existing in a space between the ultrasonic probe and the surface of the material to be inspected evaporates, it is difficult to correctly detect a flaw in the material. With this method, furthermore, it is not possible to detect a flaw in the material that is heated higher than a predetermined temperature, or to detect a flaw in the material from a remote position.